I have owned a 12 ga Mossberg 500 for years. Don't shoot it much, but when I do, it might be 50 - 100 clays a weekend at the range, a handful of times per year.

Just recently I had a cycling issue. Being handy, I did my homework and called Mossberg. They were good enough to send me replacement Cartridge Stop(s). When the package arrived, two stops were in the envelope, one for a 12 ga and one for a 20ga, they looked exactly the same, just stamped 12 and 20.

Now here is what is wild.. I take out my original Cartridge Stop and noticed it was a 20 Ga It came that way from the factory ! Are Mossberg 500 Cartridge Stops 12 vs 20 gauge the same ?

I have now replaced the old 20 ga one with the 12 gauge one and cycled through four 12 ga Snap Caps several times. The mechanism seems to work fine. Hopefully that will translate to the range, the last time I did that, the live shells failed to cycle as well as the dummies.